Cold emission cathode



XI I. 31127617 SUBSTITUTE FOR MISSING XR' A. M. SHROFF COLD EMISSION CATHODE Filed Feb. 26, 1964 INVENTOR! Afvind Maganb/va/ SHROFF 1 189- I NQLORE pmssgg United States Patent cc 3,278,789 COLD EMISSION CATHODE Arvind M. Shroif, Paris, France, assignor to CSF-Compa- The present invention relates to cold cathodes with a dielectric layer.

It is known that these cathodes comprise a thin layer of a porous dielectric such as MgO, disposed on a metallic support, for example, of aluminum. The operation of such cathodes is based on the extraction, by means of a suitable electric field, of electrons from the metallic body, these electrons penetrating the dielectric layer and producing therein an electron multiplication by avalanche whereby, these liberated electrons are emitted by the cathode due to the extraction by the aforementioned field.

It is known that to start the operation of these cathodes, it is not sutlicient to establish the extraction field by applying a voltage between the anode and the cathode but, it is necessary also to excite the cathode by bringing or applying to the surface thereof initial positive charges, by means of an excitation source supplying fast electrons, a radioactive radiation, etc. This source may be a hot filament, a radioactive body, a discharge column in a gas, a light source, etc. The operation of this source may be stopped once the operation of the cathode is started, as this operation then continues by self-maintaining or sustaining action if the potential of the cathode surface is sufficiently high.

In the known cathodes, one has utilized heretofore a source separate from the principal cathode and extracting anode system, to supply the excitation means necessary for the starting. A complication relative to the known devices results therefrom, and the present invention has as aim to avoid this complication by incorporating the maintaining or sustaining source within the structure itself of the cathode.

Known in the prior art are triple structures composed of a support made of metal such as aluminum, a very thin layer of dielectric such as alumina and an also very thin layer of pure metal with low work function, such as gold, platinum or palladium. It is known that these layers emit electrons if one applies between the metal with low work function and the support metal a relatively low voltage, of the order, for example, of volts, which creates within the very thin layer of the dielectric a very high field which extracts from the support metal electrons capable of traversing the dielectric layer by tunnel effect and traversing also the very thin layer of gold or analogous material. According to the present invention one utilizes such a structure and electrons emitted by the same to excite the cold cathode having a dielectric layer as described hereinabove, particularly by combining the metallic support of the dielectric emissive layer with the very thin layer of pure metal of the triple exciting structure.

Accordingly, the present invention consists of a quadruplc structure operating as cold cathode having a dielectric layer excited by a source incorporated into the cathode, this structure comprising a metallic suppot, a first very thin dielectric layer, a very thin layer of metal capable of being produced with great purity and having a low work function, and a second layer of porous dielectric emissive by electron multiplication, disposed on the said layer of pure metal.

Means will be provided to apply a relatively low voltage between the said layer of pure metal and the said metallic support, and to apply a relatively high voltage between an extracting anode and the said layer of pure metal.

3,278,789 Patented Oct. 11, 1966 Accordingly, it is an object of the present invention to provide a cold cathode of the type described hereinabove which obviates the shortcomings encountered with the prior art constructions.

It is another object of the present invention to provide a cold cathode which eliminates the need for separate means to start the cathode emission in cold cathodes.

A further object of the present invention resides in a cold cathode structure incorporating therein the starting means for starting the emission.

Still a further object of the present invention resides in the provision of a quadruple cold cathode structure which is simple in structure, versatile in application, and which includes as part of its structure the means necessary to start emission of the electrons from the cold cathode.

These and other objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawing which shows in the single figure thereof, for purposes of illustration only, one embodiment in accordance with the present invention.

Referring now to the single figure of the drawing which shows a schematic cross sectional view through an electron tube utilizing a cold cathode structure according to the present invention, the tube illustrated in the drawing comprises within an evacuated envelope 1, a cathode in the form of quadruple structure, and composed of: a layer 2, for example, of aluminum, preferably of a sufiicicnt thickness to serve as relatively sturdy andrigid mechanical support, for example, of the order of 1 mm.; a layer 3, of a thickness of the order of to 300 Angstroms, made of alumina (A1 0 evaporated on the aforementioned support 2 in vacuum or formed by anode oxidation; a layer 4 with a thickness of the order of 400 Angstroms, of a metal capable of being produced with great purity and having a low work function, such as gold, platinum or paladium, this layer being obtained by evaporation on the preceding layer 3; and a layer 5, made of a dielectric such as magnesia, with a thickness of the order of 50 microns, this layer being evaporated on the support 4 thereof under such well known conditions as are necessary to realize a porous layer.

In front of the surface of the layer 5, at a slight distance, for example, of 0.5 to 1 mm. is disposed an extracting anode 6, for example, in the form of a grid.

A voltage of the order of 10 volts is applied between the layers 4 and 2. from the source 7, and a voltage of the order of 200 to 300 volts is applied from the source 8 between the anode 6 and the layer 4.

The tube eventually also includes other electrodes such as the grids 9 and 10 and the plate 11, all of these electrodes being carried by conventional source (not shown) at suitable potentials with a view to produce the desired operation.

Operation The operation of the cold cathode structure according to the present invention is as follows:

In operation, the field created within the layer 3 by the source 7 extracts from the support 2 electrons which traverse the layer 3 by tunnel effect to move toward the layer 4. The application from the source 8 of an intense field within the layer 5 permits these electrons to traverse the layer 4 in such a manner that these electrons enter the layer 5 which they excite by producing the formation of positive charges at the surface thereof facing the anode 6. At the same time, the arrival of the electrons in the layer 5 gives rise to the multiplication by avalanche effect in producing an electron flow which leaves from the surface of the layer 5 and is accelerated by the field toward the anode 6. If one desires to cause the electrons to move toward other electrodes such as 9,10, and 11, the entire structure 2, 3, 4, 5 and the electrode 6 behave as a cathode; the electrode 6 being in effect in the form of a grid, a portion of the electrons traverses the meshes thereof and is directed by suitable fields toward the ulterior electrodes, as if electrons were involved issued from a con ventional cathode. However, one may also make the electrode 6 in the form of a solid plate and to utilize the tube as a simple diode.

One will note the absence of any separate source of electrons or rays to excite the cold cathode, as well as the absence of the necessity to stop such a source after the starting period.

While I have shown and described one embodiment in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of numerous changes and modifications as known to a person skilled in the art, and I therefore do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.

I claim:

1. A cold emission cathode comprising:

means forming a cathode structure and including a porous dielectric layer and a metal layer supporting said dielectric layer,

and exciting means for said cathode, integrated into said cathode structure, for creating initial positive charges on the surface of said dielectric layer.

2. A cold emission cathode comprising:

means forming a cathode structure and including a porous dielectric layer and a metal layer supporting said dielectric layer,

and means for starting the emission of electrons from said cathode structure by creating initial positive charges on the surface of said dielectric layer including exciting means formed integrally with said cathode structure.

3. A cold emission cathode structure comprising:

a porous dielectric layer,

and exciting means for the cathode essentially consisting of a metallic support, a dielectric layer on said support, and a relatively very thin layer of relatively very pure metal having a low work function.

said exciting means operating by electron emission for irradiating said first dielectrc layer thereby creating a positive charge on the surface thereof and said exciting means being integrated with said cathode structure.

4. A cold emission cathode structure comprising:

a porous dielectric layer,

and exciting means for the cathode including a rnctallic support, a dielectric layer on said support, and a relatively thin layer of relatively very pure metal having a low work function,

said exciting means operating by electron emission for irradiating said first dielectric layer thereby creating a positive charge on the surface thereof and said exciting means forming a unitary integral part of the cathode structure.

5. A cold emission cathode structure comprising:

a first porous dielectric layer,

a first metal layer supporting said first dielectric layer,

said first metal layer being relatively thin and consisting of a relatively pure metal having a relatively low work function,

a second dielectric layer supporting said first metal layer,

and a second metal layer supporting said second dielectric layer,

the assembly of said two metal layers with the second dielectric layer disposed therebetween being operable as exciting means for the assembly constituted by said first dielectric layer and said first metal layer, and said last-mentioned assembly being operable as a second dielectric layer supporting said first metal layer,

and a second metal layer supporting said second dielectric layer,

the assembly of said two metal layers with the second dielectric layer disposed therebetween being operable as exciting means for the assembly constituted by said first dielectric layer and said first metal layer, and said last-mentioned assembly being operable as a source of electrons to be emitted from the cathode structure.

7. A cold emission cathode structure comprising:

a first porous dielectric layer,

a first metal layer supporting said first dielectric layer,

said first metal layer being relatively thin and consisting of a relatively pure metal having a relatively low work function, the width of said first metal layer being of the order of hundreds of Angstroms,

a second dielectric layer supporting said first metal layer,

and a second metal layer supporting said second dielectric layer,

the assembly of said two metal layers with the second dielectric layer disposed therebetween being operable as exciting means for the assembly constituted by said first dielectric layer and said first metal layer, and said last-mentioned assembly being operable as a source of electrons to be emitted from the cathode structure.

8. A cold emission cathode structure comprising:

a first porous dielectric layer of magnesia,

a first metal layer supporting said first dielectric layer,

said first metal layer being relatively thin and consisting of a relatively pure metal having a relatively low work function,

a second dielectric layer supporting said first metal layer,

. and a second metal layer supporting said second dielec- 9. A cold emission cathode structure comprising:

a first porous dielectric layer whose width is of the order of tens of microns,

a first metal layer supporting said first dielectric layer,

said first metal layer being relatively thin and consisting of a relatively pure metal having a relatively low work function,

a second dielectric layer supporting said first metal layer,

and a second metal layer supporting said second dielectric layer,

the assembly of said two metal layers with the second dielectric layer disposed therebetween being operable as exciting means for the assembly constituted by said first dielectnic layer and said first metal layer, and said last-mentioned assembly being operable as a source of electrons to be emitted from the cathode structure.

10. A cold emission cathode structure comprising:

a first porous dielectric layer,

a first metal layer supporting said first dielectric layer,

said first metal layer being relatively thin and consisting of a relatively pure metal having a relatively low work function selected from the group consisting of gold, platinum and palladium,

a second dielectric layer of alumina supporting said first metal layer,

and a second metal layer supporting said second dielect-ric layer,

the assembly of said two metal layers with the second dielectric layer disposed therebetween being operable as exciting means for the assembly constituted by said first dielectric layer and said first metal layer, and said last-mentioned assembly being operable as a source of electrons to be emitted from the cathode structure.

11. A cold emission cathode structure comprising:

a first porous dielectric layer,

a first metal layer supporting said first dielectric layer,

said first metal layer being relatively thin and consisting of a relatively pure metal having a relatively low work function selected from the group consisting of gold, platinum and palladium,

a second dielectric layer supporting said first metal layer whose width is of the order of hundreds of Angstroms,

and a second metal layer supporting said second dielec tric layer,

the assembly of said two metal layers with the second dielectric layer disposed therebetween being operable as exciting means for the assembly constituted by said first dielectric layer and said first metal layer, and said last-mentioned assembly being operable as a source of electrons to be emitted from the cathode structure.

12. A cold emission cathode structure comprising:

a first porous dielectric layer,

a first metal layer supporting said first dielectric layer,

said first metal layer being relatively thin and consisting of a relatively pure metal having a relatively low work function selected from the group consisting of gold, platinum and palladium,

a second dielectric layer supporting said first metal layer,

and a second metal layer of aluminum supporting said second dielectric layer,

the assembly of said two metal layers with the second dielectric layer disposed therebetween being operable as exciting means for the assembly constituted by said first dielectric layer and said first metal layer,

and said last-mentioned assembly being operable as a source of electrons to be emitted from the cathode structure.

13. A cold emission cathode structure comprising:

a first porous dielectric layer,

a first metal layer supporting said first dielectric layer,

said first metal layer being relatively thin and consisting of a relatively pure metal having a relatively low work function selected from the group consisting of gold, platinum and palladium,

a second dielectric layer supporting said first metal layer,

and a second metal layer supporting said second dielectric layer whose width is substantially greater than the width of each other layer,

the assembly of said two metal layers with the second dielectric layer disposed therebetween being operable as exciting means for the assembly constituted by said first dielectric layer and said first metal layer, and said last-mentioned assembly being operable as a source of electrons to be emitted from the cathode structure.

14. A cold emission cathode structure comprising:

a first porous dielectric layer,

a first metal layer supporting said first dielectric layer,

said first metal layer being relatively thin and corn sisting of a relatively pure metal having a relatively low work function,

a second dielectric layer supporting said first met layer,

and a second metal layer supporting said second dielectric layer,

the assembly of said two metal layers withv the second dielectric layer disposed therebetween being operable as exciting means for the assembly constituted by said first dielectric layer and said first metal layer, and said last-mentioned assembly being operable as a source of electrons to be emitted from the cathode structure,

and extracting electrode means facing said first dielectric layer,

means for applying a relatively low voltage between said two metal layers with the positive polarity applied to the first metal layer,

and means for applying a relatively high voltage between said ex-tracting electrode means and said first metal layer, with the positive polarity applied to said extracting electrode means.

15. A cold emission cathode structure comprising:

a first porous dielectric layer of magnesia whose width is of the order of tens of microns,

a first metal layer supporting said first dielectric layer,

said first metal layer being relatively thin and consisting of a relatively pure metal having a relatively low work function selected from the group consisting of gold, platinum and palladium, the width of said first metal layer being of the order of hundreds of Angstroms,

a 1second dielectric layer supporting said first metal ayer,

and a second metal layer supporting said second dielectric layer,

the assembly of said two metal layers with the second dielectric layer disposed therehetween being operable .as exciting means for the assembly constituted by said first dielectric layer and said first metal layer, and said last-mentioned assembly being operable as a source of electrons to be emitted from the cathode structure,

and extracting electrode means facing said first dielectric layer,

means for applying a relatively low voltage between said two metal layers with the positive polarity applied to the first metal layer,

and means for applying a relatively high voltage between said extracting electrode means and said first metal layer, with the positive polarity applied to said extracting electrode means.

16. A cold emission cathode structure comprising:

a first porous dielectric layer,

a first metal layer supporting said first dielectric layer,

said first metal layer being relatively thin and consisting of a relatively pure metal having a relatively low work function selected from the group consisting of gold, platinum and palladium,

a second dielectric layer of alumina supporting said first metal layer whose width is of the order of hundreds of Angstroms,

and a second metal layer of aluminum supporting said second dielectric layer whose width is substantially greater than the width of each other layer,

the assembly of said two metal layers with the second dielectric layer disposed therebetween being operable as exciting means for the assembly constituted by said first dielectric layer and said first metal layer, and said last-mentioned assembly being operable as a source of electrons to be emitted from the cathode structure,

and extracting electrode means facing said first dielectric layer,

means for applying a relatively low voltage between said two metal layers witli'the positive polarity applied to the first metal layer,

and means for applying a relatively high voltage between said extracting electrode means and said first metal layer, with the positive polarity applied to said extracting electrode means.

, 17. A cold emission cathode structure comprising:

a second dielectric layer supporting said first metal layer,

and a second metal layer supporting said second dielectric layer,

the assembly of said two metal layers with the second dielectric layer disposed therebetween being oper able as exciting means for the assembly constituted by said first dielectric layer and said first metal layer, and said last-mentioned assembly being operable as a source of electrons to be emitted from the cathode structure.

18. A cold emission cathode structure comprising:

a first porous dielectric layer of magnesia whose width is of the order of tens of microns,

a first metal layer supporting said first dielectric layer,

said first metal layer being relatively thin and consisting of a relatively pure metal having a relatively low work function,

a second dielectric layer supporting layer,

and a second metal layer supporting said second dielectric layer,

the assembly of said two metal layers with the second dielectric layer disposed therebetween being operable as exciting means for the assembly constituted by said first dielectric layer and said first metal layer, and said last-mentioned assembly being operable as a source of electrons to be emitted from the cathode structure.

19. A cold emission cathode structure comprising:

a first porous dielectric layer,

a first metal layer supporting said first dielectric layer,

said first metal layer being relatively thin and consisting of a relatively pure metal having a relatively low work function selected from the group consisting of gold, platinum and palladium,

a second dielectric layer of alumina supporting said first metal layer whose width is of the order of hundreds of Angstrorns,

and a second metal layer supporting said second dielectric layer,

the assembly of said two metal layers with the second dielectric layer disposed therebetwecn being operable as exciting means for the assembly constituted by said first dielectric layer and said first metal layer, and said last-mentioned assembly being operable as a source of electrons to be emited from the cathode structure.

20. A cold emission cathode structure comprising:

a first porous dielectric layer,

a first metal layer supporting said first dielectric layer,

said first metal layer being relatively thin and consisting of a relatively pure metal having a relatively low work function selected from the group consisting of gold, platinum and palladium,

a second dielectric layer supporting said first metal layer,

and a second metal layer of aluminum supporting said second dielectric layer whose width is substantially greater than the width of each other layer,

said first metal the assembly of said two metal layers with the second dielectric layer disposed therebetween being operable as exciting means for the assembly constituted by i said first dielectric layer and said first metal layer, and said last-mentioned assembly being operable as as a source of electrons to be emitted from the cathode structure.

21. A cold emission cathode structure comprising:

a porous dielectric layer of magnesia whose Width is of the order of tens of microns,

a metal layer supporting said dielectric layer, said first metal having a width of the order of hundreds of Angstroms and consisting of a relatively pure metal having a relatively low work function selected from the group consisting of gold, platinum and palladium,

21 second dielectric layer of alumina supporting said first metal layer whose width is of the order hundreds of Angstroms,

and a second metal layer of aluminum supporting said second dielectric layer whose width is substantially greater than the width of the other layers,

the assembly of said two metal layers with the dielectric layer disposed therebetween being operable as exciting means for the assembly constituted by said first dielectric layer and said first metal layer, and said last-mentioned assembly being operable as a source of electrons to be emitted from the cathode 1 structure.

22. A cold emission cathode structure comprising:

a porous dielectric layer of magnesia whose width is of the order of tens of microns,

a metal layer supporting said dielectric layer, said first metal having a width of the order of hundreds of Angstroms and consisting of a relatively pure metal having a relatively low work function selected from the group consisting of gold, platinum and palladium,

a second dielectric layer of alumina supporting said first metal layer whose width is of the order hundreds of Angstroms,

and a second metal layer of aluminum supporting said second dielectric layer whose width is substantially greater than the width of the other layers,

the assembly of said two metal layers with the dielec tric layer disposed therebetween being operable as exciting means for the assembly constituted by said first dielectric layer and said first metal layer, and said last-mentioned assembly being operable as a source of electrons to be emitted from the cathode structure,

and extracting electrode means facing said first dielectric layer,

means for applying a relatively low voltage between said two metal layers with the positive polarity applied to the first metal layer,

and means for applying a relatively high voltage be tween said extracting electrode means and said first metal layer, with the positive polarity applied to said extracting electrode means.

References Cited by the Examiner UNITED STATES PATENTS JOHN W. HUCKERT, Prz'nmry Examiner.

A. 1, JAMES, Assistant Examiner. 

16. A COLD EMISSION CATHODE STRUCTURE COMPRISING: A FIRST POROUS DIELECTRIC LAYER, A FIRST METAL LAYER SUPPORTING SAID FIRST DIELECTRIC LAYER, SAID FIRST METAL LAYER BEING RELATIVELY THIN AND CONSISTING OF A RELATIVELY PURE METAL HAVING A RELATIVELY LOW WORK FUNCTION SLEECTED FROM THE GROUP CONSISTING OF GOLD, PLATINUM AND PALLADIUM, A SECOND DIELECTRIC LAYER OF ALUMINA SUPPORTING SAID FIRST METAL LAYER WHOSE WIDTH IS OF THE ORDER OF HUNDREDS OF ANGSTROMS, AND A SECOND METAL LAYER OF ALUMINUM SUPPORTING SAID SECOND DIELECTRIC LAYER WHOSE WIDTH IS SUBSTANTIALLY GREATER THAN THE WIDTH OF EACH OTHER LAYER, THE ASSEMBLY OF SAID TWO METAL LAYERS WITH THE SECOND DIELECTRIC LAYER DISPOSED THEREBETWEEN BEING OPERABLE AS EXCITING MEANS FOR THE ASSEMBLY CONSTITUTED BY SAID FIRST DIELECTRIC LAYER AND SAID FIRST METAL LAYER, AND SAID LAST-MENTIONED ASSEMBLY BEING OPERABLE AS A SOURCE OF ELECTRONS TO BE EMITTED FROM THE CATHODE STRUCTURE, AND EXTRACTING ELECTRODE MEANS FACING SAID FIRST DIELECTRIC LAYER, MEANS FOR APPLYING A RELATIVELY LOW VOLTAGE BETWEEN SAID TWO METAL LAYERS WITH THE POSITIVE POLARITY APPLIED TO THE FIRST METAL LAYER, AND MEANS FOR APPLYING A RELATIVELY HIGH VOLTAGE BETWEEN SAID EXTRACTING ELECTRODE MEANS AND SAID FIRST METAL LAYER, WITH THE POSITIVE POLARITY APPLIED TO SAID EXTRACTING ELECTRODE MEANS. 